The polymers widely used at present to fabricate self-polishing marine antifouling paints are polymers that contain pendant organotin ester (e.g., acrylate) groups. Indeed, marine antifouling paints based on organotin acrylate polymers have dominated the market for over 20 years. The organotin acrylate-containing polymers, when formulated into a paint and applied to the bottom (i.e., hull) of a marine vessel, hydrolyze in seawater to release an organotin compound (usually tributyltin oxide) that is an active antifoulant preventing marine plants and other organisms from adhering to the vessel bottom. This fouling (i.e., undesirable attachment of organisms to a marine surface) results in increased drag which can significantly increase fuel consumption and, therefore, operating costs. In addition, movement of the vessel through water erodes the paint surface to constantly expose a fresh polymer surface to the hydrolytic effect of seawater. This constant erosion of the paint surface results in the development and maintenance of a smooth surface on the immersed exterior of the marine vessel, which also contributes to reduced drag and greater efficiency.
Further, these paints, properly formulated and applied, have the ability to remain effective for 5 years. This is important because large vessels (e.g., oil tankers and container ships) are dry-docked at 5-year intervals for routine maintenance and inspection; it is most convenient to repaint the hull exterior during these periodic maintenance episodes.
Although effective, the use of organotin-containing polymers in antifouling marine paints has come under attack due to the adverse effect that organotin compounds are believed to have upon the marine environment. The U.S. Environmental Protection Agency (EPA) has significantly restricted the continued use of organotin compounds and the Marine Environmental Protection Committee (MEPC) of the International Maritime Organization (IMO), a unit of the United Nations, has recently approved a resolution to phase out and eventually prohibit the use of organotin-containing materials in antifouling paints.
As a result, there is a need in the art for improved erodible antifouling paint compositions comprising film-forming polymers that are free of tin, while retaining the good antifouling and self-polishing properties as well as the longevity of the organotin-containing antifouling paints.
U.S. Pat. No. 4,593,055 discloses that silylacrylate copolymers of formula where X is H or CH3 
                R is selected from the group consisting of —SiR′nR″3-n or —Si(OR′nR″3-n)3 wherein R′ and R″ are independently straight or branched chain alkyl C1-C10 or phenyl and n=0-3 are useful to formulate marine antifoulant coatings. The organosilylacrylate component is present in the Examples in amounts ranging from 20 to 40 mole percent.        
U.S. Pat. No. 5,436,284 discloses that copolymers containing silylacrylate units are useful to formulate marine antifoulant coating compositions. The Examples (Monomer A4 in Table 3) show arylsilylacrylate copolymers containing 45 and 50 percent by weight of arylsilylacrylate component.
EP 1 127 925 A1 discloses polymeric binders for marine antifoulant paints that contain triarylsilylacrylate groups. The patent teaches that the polymer contains from 20 to 70 percent by weight of triarylsilyl(meth)acrylate, preferably from 30 to 65 percent by weight, and more preferably from 50 to 60 percent by weight.
U.S. Pat. No. 5,795,374 discloses marine antifoulant paints formulated from polymers containing triorganosilyl groups; Monomer M4 is diphenyl-t-butylsilyl acrylate, which is employed in an amount of 10 wt % to make polymer S4. This weight represents about 3 mole %, which, as will be seen from the data, is too low for proper erosion of the polymer film.
U.S. Pat. No. 4,593,055 discloses that marine antifouling paints can be formulated from copolymers containing a hydrolysable triorganosilyl residue, including an arylsilyl residue. The preferred level of triorganosilyl acrylate or methacrylate in the copolymer is from 25 to 40 mole percent.
WO91/14743 discloses erodible marine antifoulant paints with polymeric binders having organosilyl functional groups with the paint having increased storage stability when containing antifouling agents containing copper or zinc. Increased paint storage stability is obtained by using monoamine and quaternary ammonium compounds which inhibit gelation associated with such binders and copper or zinc containing antifouling agents.
Additional patents that concern triorganosilyl containing polymers as binders for marine antifouling paints are: JP 63-057676 which discloses adding a polymethyl silsesquioxane powder for stability when the paint has copper containing antifoulant compounds; EP 714957 B1 which discloses a copolymer containing a triorganosilylacrylate and as an essential ingredient a monomer containing an acryloyloxy, a methacryloyloxy, maleinoyloxy or fumaroyloxy group; EP 0802243 B1 which discloses a marine antifouling paint having an organosilylacrylate based polymeric binder and a rosin compound to improve the erosion rate of the paint;
The following listed patents and applications further disclose terpolymers comprising triorganosily(meth) acryloyl pendant groups useful as binders in marine antifouling coatings: EP 0646630B1, EP 0775733A1, EP 1016681A2, EP 1127925A1, JP 8-269389A, U.S. Pat. No. 4,594,365, U.S. Pat. No. 5,436,284, U.S. Pat. No. 5,795,374, WO 84/02915, WO 91/14743, WO 0077102A1.